U.S. Pat. No. 7,995,191 B1 to Sandusky (hereinafter “Sandusky”) and assigned to Sandia Corporation discloses a scannerless 3-D imaging apparatus which utilizes an amplitude modulated continuous wave light source to illuminate a field of view containing a desired target. Backscattered light from the target is passed through one or more loss modulators which are modulated at the same frequency as the light source, but with a phase delay δ which can be fixed or variable. The backscattered light is demodulated by the loss modulator and detected with a CCD, CMOS or focal plane array (FPA) detector to construct a 3-D image of the target. The scannerless 3-D imaging apparatus, which can operate in the eye-safe wavelength region 1.4-1.7 μm and which can be constructed as a flash LADAR, has applications for vehicle collision avoidance, autonomous rendezvous and docking, robotic vision, industrial inspection and measurement, 3-D cameras, and facial recognition.
Unlike the current invention, Sandusky applies only to active imaging and does not use heterodyning. Passive imagery is not sensed at all. For active imaging, Sandusky does not have the background light immunity advantages of HSAAI the Heterodyne Starring Array Active Imager (HSAAI) and is not multi-spectral.
U.S. Patent Application Pub. No. US 2005/0046857 A1 to Bingham et al. (hereinafter “Bingham”) discloses systems and methods for spatial-heterodyne interferometry for transmission (SHIFT) measurements. A method includes digitally recording a spatially heterodyned hologram including spatial heterodyne fringes for Fourier analysis using a reference beam, and an object beam that is transmitted through an object that is at least partially translucent; Fourier analyzing the digitally recorded spatially-heterodyned hologram, by shifting an original origin of the digitally recorded spatially-heterodyned hologram to sit on top of a spatial-heterodyne carrier frequency defined by an angle between the reference beam and the object beam, to define an analyzed image; digitally filtering the analyzed image to cut off signals around the original origin to define a result; and performing an inverse Fourier transform on the result.
Bingham uses heterodyning in the sense of mixing beams for a hologram application but does not use photo detectors or waveguide technology. Further, the objective of Bingham is interferometry and not imaging, and real-time multi-spectral narrow band imagery with high sensitivity is not provided. Both the apparatus and objective are very different from the invention described in this application. In addition, Bingham does not provide any passive imagery.
U.S. Pat. No. 6,664,529 B2 to Pack et al. and assigned to Utah State University (hereinafter “Pack”) discloses a 3D Multispectral Lidar. The system comprises a laser transmitter light source, a laser detection assembly, optics that couple the outgoing and incoming laser signals, a digital camera assembly for collecting passive light, a position and orientation system, and processing hardware. The system provides real-time georectified three dimensional images and topography using an airborne platform. The system collects time-synchronous Lidar range and image data in an optical receiver. The individual images are then mosaiced and orthorectified in real-time. The Lidar range data and image data are then coupled to a position and orientation system to transform the three-dimensional range images to a single geographically referenced multispectral three-dimensional image
Pack includes direct detection passive imaging and does not employ either waveguide technology or heterodyning. Pack does not provide the multi-spectral and highly sensitive imagery of the invention described in this application.
U.S. Pat. No. 7,049,597 B2 to Bodkin (hereinafter “Bodkin”) discloses a common aperture, multi-mode optical imager for imaging electromagnetic radiation bands from a field of two or more different wavelengths is described. Fore-optics are provided to gather and direct electromagnetic radiation bands forming an image into an aperture of the multi-mode optical imager. The image is divided into two different wavelength bands, such as visible light and long-wave infrared. The first wavelength band (e.g., visible light) is detected by a first detector, such as a CCD array, for imaging thereof. The second wavelength band (e.g., long-wave infrared) is detected by a second detector, such as an uncooled microbolometer array, for imaging thereof. Additional optics may be provided for conditioning of the first and second wavelength bands, such as such as for changing the magnification, providing cold shielding, filtering, and/or further spectral separation.
Bodkin uses direct detection and not heterodyning and does not provide the sensitivity or ability to image very narrow spectral bands that is provided by the invention described in this application. Further, the multiple spectral bands are independently imaged on separate detector arrays rather than gathered by optical collection elements and waveguided to spectral filters and then to heterodyned detectors. The current invention HSAAI provides the capability to switch spectral band selection, the ability to image many and not just two spectral bands, and sensitivity for narrow spectral bands not possible with the direct detection method of the App.
U.S. Pat. No. 6,931,031 B2 to Williams et al. and assigned to Aston University (hereinafter “Williams”) discloses a dual wavelength optical fiber distributed feedback laser comprising a pump laser coupled to a birefringent fiber in which a first grating device (two co-located single phase-shift fiber Bragg gratings (FBGs)) is provided. The grating device gives the laser two potential lasing modes in each of two orthogonal polarization states. A polarization mode coupling FBG selects two orthogonally polarized modes on which the laser oscillates. In a photonic data carrying signal source, the laser is coupled to a polarization dependent, optical modulator operable to apply a modulation, at a data signal frequency, to one polarization mode of the laser output. In an optical waveguide based electronic signal transmission system the modulated and unmodulated polarization modes output from the source are transmitted across a fiber transmission line to a polarizing optical fiber in which the two modes heterodyne to generate an electronic carrier signal in the optical domain.
Williams uses some of the same basic tools as the current invention like Bragg gratings and waveguide modulators. However, the objective is completely different in that these components are used for the generation of laser light and not for imaging. Further, the basic tool set (spectral filtering, waveguiding in fibers) is implemented very differently to address the different objective.
U.S. Pat. No. 5,146,358 to Brooks and assigned to PYR Systems, Inc. (hereinafter “Brooks”) discloses an optical communication system for disseminating information. The systems include a source of continuous wave laser light and one or more acoustic beams which are frequency or amplitude modulated by data. The laser light beam and the acoustic beams are input to an acousto-optical modulator for producing an undiffracted laser light beam and one or more diffracted laser light beams. The diffracted laser light beams are frequency shifted from the undiffracted laser light beam and contain the data to be transmitted. The diffracted and undiffracted beams are combined and transmitted over an optical fiber for demodulation at a distant location by a receiver. The receiver includes a photodiode which heterodynes the diffracted and undiffracted beams and produces signals having the frequencies of the acoustic beams. Tuning circuitry separates the signals and demodulators reconstruct the data transmitted. By using two such communication systems with a single optical fiber and by allocating the available bandwidth, simultaneous, bidirectional multi-channel communications are achieved.
Brooks uses many of the same component parts as the invention described in this application but the objective and implementation of Brooks is very different. Brooks addresses communications and not imaging and does not use heterodyning in photo detectors to provide highly sensitive, multi-spectral images.
U.S. Pat. No. 7,667,824 issued to Moran discloses a range-gated sphearography system and related methods that includes at least one imaging detector coupled to a laser light source.
Moran implements surface vibration sensing by employing range gated techniques along with interferometers. Aside from implementing a different function than HSAAI, Moran does not use heterodyning, does not implement a starring array, and cannot be used for passive imaging.
U.S. Pat. No. 7,449,673 issued to Chuang, et al. discloses a system and method for reducing peak power of a laser pulse and reducing speckle contrast of a single pulse comprising a plurality of elements oriented so as to split a pulse or pulses transmitted from a light source.
Chuang achieves one of many benefits of HSAAI, namely reduction of speckle in active imagery. However, implementation is via splitting of optical beams, so the method is very different from HSAAI. In addition, other benefits of HSAAI are not disclosed in Chuang.
U.S. Pat. No. 7,233,392 issued to Margalith, et al. discloses a spectral imaging device including a optical parametric oscillator that can be tuned across a wide range of wavelengths while illuminating a target.
While HSAAI shares the ability to vary wavelength of operation, the waveguide method used in HSAAI is different from Margalith. Also, HSAAI discloses other benefits, like heterodyne detection.
Waveguide technology is also prior art. Of the several waveguide technologies available to implement the HSAAI, silicon is the most mature. The silicon waveguide technology was originally developed to implement fiber optic communications. Component parts developed and tested include light collectors that gather free-air light into a waveguide, waveguide designs that can turn sharp corners and be overlaid at right angles without cross-talk, polarization diversifiers to convert input light into one electromagnetic mode for waveguide transmission, interferometers that can also be used as optical switches, spectral resonators (generally in the form of one or more rings or racetracks), efficient light splitters and couplers, and waveguide-to-photo detector interfaces that currently provide a 60 Gigahertz (GHz) temporal bandwidth.